1. Field of the Invention
The invention relates to motor control apparatus and, more particularly, to a motor control apparatus for a railway switch machine. The invention also relates to a two-terminal control apparatus for a two-terminal reversible motor.
2. Background Information
In order to optionally switch a railroad train operating on a first track to a second, merging track, it is typical to provide a switch with a pair of xe2x80x9cswitch pointsxe2x80x9d which are selectively movable horizontally to deflect the train toward one or the other of the tracks. The switch can encompass a pair of switch rail lengths of the second track which extend several feet in length with the switch points being essentially tapered end sections of those rail lengths. The switch points, typically labeled as xe2x80x9cnormalxe2x80x9d and xe2x80x9creversexe2x80x9d, are selectively movable back and forth between a pair of stock rails. These provide a normal position in which the train is directed toward the first track by the normal switch point being positioned against a first rail of the first track, and a reverse position in which the train is directed toward the second track by the reverse switch point being positioned against the opposite rail of the first track.
The switch points are typically attached to each other via a plurality of tie rods, at least one of which doubles as a switch throw rod. The throw rod is driven by a remotely controlled electrical switch machine, or, in some instances, by a hand lever operated switch machine, between extended and retracted positions. Depending upon the side of the track on which the switch machine is placed, the extended position can be the normal or the reverse condition of the switch points, and vice versa for the retracted position.
Switch machines employ reversible electric motors to drive a series of gears which are attached to the throw rod. Depending upon the control signals received at the switch machine, the motor is driven one direction or the other to either extend or retract the throw rod and, thus, move the switch points between normal and reverse switching positions. Lock connecting rods are also attached to the switch points. The lock connecting rods passively move back and forth with the switch points and cooperate with locking elements in the machine housing to lock the switch into a normal or a reverse switch position.
Referring to FIG. 1, a switch point adjuster 2 is schematically depicted. The exemplary switch point adjuster 2 utilizes two separate rods 3, 4 and a frog 5, although a single operating rod (not shown) may be employed. The exemplary switch point adjuster 2 is located at the center of the track 6, although other such adjusters may be employed on the left side (with respect to FIG. 1) and opposite the switch machine 8. The first rod 3 connects the switch point adjuster 2 to the frog 5, and the second rod 4 connects the switch point adjuster 2 to the operating bar 10 of the switch machine 8. Thus, when the switch machine 8 throws six inches, the slack is taken up in the switch point adjuster 2 so that the frog 5 is only moved its required amount. Both operating rods 3, 4 are supported by support rollers (not shown).
As shown in FIG. 2, a railroad switch includes a pair of switch points 12,14 which are linked by one or more tie rods 16. The switch points 12,14 are selectively movable between a xe2x80x9cnormalxe2x80x9d position (as shown) and a xe2x80x9creversexe2x80x9d position. In the illustrated normal position, the switch point 12, commonly called the normal switch point, is positioned against a stationary stock left rail 18, and the switch point 14, commonly called a reverse switch point, is moved away from a stationary stock right rail 20. The stock left and right rails 18 and 20 are anchored to a plurality of cross ties 22 via rail anchors 24 in a conventional manner. In a normal position, the normal switch point 12 directs a train entering the railroad switch straight through the intersection via the right stock rail 20 and the switch point 12, which tapers outward into a straight left rail 26 past the switch.
In a reverse position (not shown) both the normal switch point 12 and the reverse switch point 14 are moved to the right (with respect to FIG. 2) with the normal switch point 12, thus, moving away from the stock left rail 18 and the reverse switch point 14 moving to a position against the stock right rail 20. The reverse switch point 14 is then in a position to direct the train to the left via the left rail 18, which curves to the left past the switch, and via the reverse switch point 14, which tapers outward to a curved right track 28 past the switch.
The switch points 12 and 14 are selectively moved via a switch machine 30. The switch machine 30 includes a reversible electric motor (M) 31 (shown in hidden line drawing) in a motor housing 32. The motor 31 is connected to drive a series of gears 33,34,35 (shown in hidden line drawing) which, in turn, drive a throw bar 36 (shown in hidden line drawing), either to the left or the right (with respect to FIG. 2). The throw bar 36 is connected to a throw rod 38 via a linkage 40. The throw rod 38, in turn, is connected to the tie rod 16 via a switch basket 41. The switch basket 41 is internally threaded to receive threads 42 on the throw rod 38, in order that the switch point position at either end of travel of the throw rod 38 is adjustable. For example, a typical stroke length for the throw bar 36 would be approximately five inches.
Historically, switch machine motor controls employed mostly 3-wire or wire control for permanent magnet or wound field motors, respectively.
In one system, power is switched to a switch machine motor (M) 42, as shown in FIG. 3, using two vital relays (not shown), the Normal Switch Relay (NSR) and the Reverse Switch Relay (RSR). Input power for the motor 42 is controlled by normal relay contacts 44,45 and reverse relay contacts 46,47. The contacts 44,45,46,47 are connected in a manner to invert the polarity of the power to the motor 42 depending upon which one of the two vital relays is energized. With both relays de-energized, the normally open contacts 44,45,46,47 open the circuit on both the input and output sides thereof. This protects the input power source from a lighting strike at the switch machine, although it does nothing to stop a stray voltage from operating the motor 42 inadvertently.
In a switch machine, linear motion of the mechanism moving the points (such as 12 and 14 of FIG. 2) is converted into rotary motion. Rotary operated cam switches, in turn, are used to open the motor circuit at the end of the stroke and steer current to change direction. The three-wire control circuit of FIG. 3 includes cam switch (CSw1) 48 and cam switch (CSw2) 49. For normal rotation, CSw1 is closed for most of the cycle and, then, opens at the end of the cycle to open the motor circuit and stop the motor 42. For reverse rotation, CSw2 is closed for most of the cycle and, then, opens at the end of the cycle to open the motor circuit and stop the motor 42.
U.S. Pat. No. 4,756,494 discloses vital two-wire switch control circuits for a railroad switch machine, which is operable to either of two directions depending upon the polarity of energy applied thereto. A mechanically-interlocked, reverse-acting, dual-coil contactor is used to alternately establish positive or negative current paths to a permanent magnet motor. Other reverse motor contacts and normal motor contacts allow energization of coils of the reversing contactor which coils have associated normal and reverse motor contacts.
U.S. Pat. No. 5,747,954 discloses a two-terminal configuration having contacts at the terminals of the motor. An electronic controller circuit for the power down function of a highway crossing guard mechanism eliminates the xe2x80x9cpumpingxe2x80x9d condition that can cause undue stress and damage to the guard mechanism. For the up direction, power is supplied through a contact to the motor and through another contact from the motor. At approximately 90xc2x0, a controller contact opens and other contacts drop to xe2x80x9cbxe2x80x9d positions. One contact feeds power to a hold clear solenoid coil that sets the brake for the crossing gate arm. Then, for power down operation, power is supplied to the motor through a MOSFET and diode of a power down module until, at approximately 45xc2x0, another contact is opened.
U.S. Pat. No. 5,806,809 discloses a switch point detection system and method that uses a series of proximity detectors positioned proximate the switch point(s) of a railroad switch. A switch machine and a motor are connected by three wires to a biased neutral controller.
U.S. Pat. No. 5,412,369 discloses a two-wire distribution system having two-wire transmission lines for electrical loads.
U.S. Pat. No. 4,703,303 discloses a sold state railroad gate controller having a logic circuit.
In known switch machine motor controls, the relay contacts are not protected from arcing due to switching direct current (DC) into an inductive load (i.e., the motor), and DC power is applied continuously to the relay contacts. Energizing the relay applies this power to the switch machine motor. As the contacts come together, a small arc is produced between the contacts as the inrush current flows to start turning the motor. If the relay is de-energized while the motor is running, then the arc will be much larger, thereby causing permanent damage or erosion to the contacts. Accordingly, there is room for improvement.
The present invention provides improvements in the control of motors for railway switch machines.
As one aspect of the invention, a control apparatus for a railway switch machine comprises a power source having a voltage, and a circuit. The circuit includes means for inputting the voltage from the power source, means for inputting a normal signal and a reverse signal, two output terminals for electrical connection to two input terminals of a reversible motor of the switch machine, and output means for: (a) outputting the voltage to the two output terminals in response to the normal signal, (b) outputting an inverted polarity of the voltage to the two output terminals in response to the reverse signal, and (c) shorting the two output terminals in response to absence of both of the normal and reverse signals.
Preferably, the output means includes a plurality of relays having a plurality of contacts, and means employing the normal and reverse signals of the means for inputting for preventing switching of the contacts of the relays when the voltage or the inverted polarity of the voltage is applied to the input terminals of the reversible motor.
Also, the output means may include means for closing the contacts of the relays before the voltage or the inverted polarity of the voltage is applied to the input terminals of the reversible motor.
Further, the output means may include means for opening the contacts of the relays after the voltage or the inverted polarity of the voltage is removed from the input terminals of the reversible motor.
As another refinement, the output means may include means for opening the contacts of the relays after the reversible motor is de-energized and has stopped rotating.
The output means may include means for preventing switching of the contacts of the relays for a predetermined time after the voltage or the inverted polarity of the voltage is removed from the input terminals of the reversible motor in order to prevent the switching when the reversible motor is rotating.
Preferably, the relays include a normal relay for outputting the voltage to the two output terminals in response to the normal signal, and a reverse relay for outputting the inverted polarity of the voltage to the two output terminals in response to the reverse signal, and the output means further includes means for preventing energization of the normal and reverse relays at the same time.
As another aspect of the invention, a control apparatus for a motor of a railway switch machine comprises a power source having first and second outputs; a first relay including a first pole having double throw contacts, and including a second pole having at least one contact, with the first pole of the first relay being electrically connected to a first input of the motor, and with a first contact of the first pole of the first relay being electrically connected to the first output of the power source; a second relay including a first pole having double throw contacts, and including a second pole having at least one contact, with the first pole of the second relay being electrically connected to a second input of the motor, with a second contact of the first pole of the first relay being electrically connected to: (a) a second contact of the first pole of the second relay, (b) the second pole of the first relay, and (c) the second pole of the second relay, and with the contact of the second pole of the first relay being electrically connected to: (a) the contact of the second pole of the second relay, and (b) the second output of the power source; means for inputting first and second signals; and means employing the first and second signals for controlling energization of the first or second relays, in order that: (a) energization of the first relay electrically connects the first output of the power source with the first input of the motor through the first contact and the first pole of the first relay, and electrically connects the second output of the power source with the second input of the motor through the contact and the second pole of the first relay and through the second contact and the first pole of the second relay, (b) energization of the second relay electrically connects the first output of the power source with the second input of the motor through the first contact and first pole of the second relay, and electrically connects the second output of the power source with the first input of the motor through the contact and the second pole of the second relay and through the second contact and the first pole of the first relay; and, otherwise, (c) energization of neither the first relay nor the second relay electrically connects the first input to the second input of the motor through the first pole and the second contact of the first relay and through the second contact and the first pole of the second relay.